Engines may be configured with an oxygen sensor coupled to an intake passage for determining the oxygen content of fresh intake air. In particular, the sensor measures the partial pressure of oxygen in the aircharge following equilibration. The aircharge amount may be further corrected for the presence of diluents which can react with oxygen at the sensor, thereby affecting the sensor's output. For example, the oxygen sensor output is corrected for the presence of humidity, hydrocarbons from EGR, purge fuel vapors, crankcase ventilation fuel vapors, etc. One example of such an approach is shown by Surnilla et al. in US patent application 20140251285.
The corrected aircharge estimate can then be used for controlling engine fueling. However, the inventors herein have recognized potential issues with such an approach for aircharge estimation. As one example, while the aircharge estimate may be correct for fueling control, it may be incorrect for torque estimation. This is because the diluent hydrocarbons that are corrected for during the aircharge estimation participate in cylinder combustion and therefore contribute towards torque production. Therefore, if the diluent corrected aircharge estimate is used for torque control, it may result in excess torque, affecting drivability. In addition, even small errors in the estimation of the diluents can cause significant errors in engine aircharge estimation, and thereby engine fuel and torque estimation. Another potential issue is that for learning actual (versus nominal) injector delivery requires the other sources of fuel (such as reductants) and diluents to be disabled. Specifically, both the injector learning and aircharge learning requires EGR, purge, and crankcase ventilation to be disabled. As a result, a window for performing adaptive learning, such as adaptive learning of fuel and diagnostics of the oxygen sensor, is limited.
In one example, at least some of the above issues may be addressed by a method for an engine, comprising: while flowing one or more diluents into an engine, adjusting engine fueling responsive to an output of an intake oxygen sensor independent of the diluents, and learning an adaptive fuel correction. In this way, fuel and torque may be estimated more accurately using the intake oxygen sensor. In addition, adaptive fuel learning may be performed without the need to disable EGR, fuel vapor purge, or crankcase ventilation.
As an example, during conditions when the engine is operating with one or more of EGR, purge, or crankcase ventilation enabled, a controller may estimate a net oxygen content of the intake aircharge based on the output of an oxygen sensor coupled to an intake passage of the engine. The net oxygen content may not need to be compensated for the presence of diluents such as the purge or crankcase fuel vapors and the EGR. In particular, the inventors have recognized that a catalyzing oxygen sensor measures the net air concentration that needs a matching amount of fuel. Consequently, the air charge estimation based on the output of the oxygen sensor is insensitive to (and therefore independent of) the presence of diluents in the air. While the unadjusted output of the oxygen sensor is used for fuel control, the oxygen output corrected for the presence of diluents is then used for engine torque control. For example, the oxygen output may be corrected based on an EGR and/or humidity measurement (measured by the oxygen sensor or a dedicated sensor), and an aircharge estimated based on the corrected output may be used for torque control. In addition, while flowing the EGR, purge, or PCV hydrocarbons, adaptive fuel learning may be performed. For example, a fuel injector offset may be learned and/or MAF sensor offsets may be learned.
In this way, the output of an intake oxygen sensor may be used for fuel and torque control. In essence, the oxygen sensor is advantageously used as an intake manifold pressure sensor for aircharge estimation during selected conditions. The technical effect of using the unadjusted output of the oxygen sensor for estimating an aircharge that is used for fuel control is that engine fueling can be accurately controlled independent of diluent presence. In addition, adaptive fuel learning can be performed while EGR, purge, or PCV vapors are flowing, improving the window of adaptive fuel learning. The technical effect of using a diluent adjusted output of the oxygen sensor for estimating an aircharge that is used for torque control is that fuel and torque can each by accurately controlled using the output of the same oxygen sensor. In addition, the output of the intake oxygen sensor may be used to correct or confirm the output of a manifold pressure or engine air flow rate sensor. By enabling adaptive learning to be performed over a wider range of operating conditions, including while fuel vapors are flowing into the engine, adaptive learning can be completed more effectively over a drive cycle. Overall, engine performance is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.